1. Field of the Invention
The present invention relates to a headlamp device for a vehicle, and more particularly, to a headlamp device with adjustable brightness and a luminance control method for the headlamp device.
2. Description of the Related Art
All vehicles are required to be equipped with headlamps. An attempt to improve the driver's field of vision within the confines of the law is sometimes made. For example, an AFS (Adaptive Front-Lighting System), in which the optical axis moves in the direction in which the vehicle is steered by the driver when the vehicle is moving, is known.
Japanese Patent Application Publication No. 2002-193027 (JP-A-2002-193027) discloses a light distribution control device which, on detecting the entrance of the vehicle into a registered control area, performs light distribution control that is registered for the control area. JP-A-2002-193027 discloses a technology to perform control with consideration for pedestrians and oncoming vehicles by shining light on a laterally elongated area in a residential district with many pedestrians so that the driver can see pedestrians easily, turning on the headlamps automatically on roads which are dark day and night such as forest roads, and reducing the amount of light in the vertical direction and illuminating the right and left sides of the vehicle intensively in, for example, a parking lot.
Japanese Patent Application Publication No. 2004-291816 (JP-A-2004-291816) discloses a headlight luminance control device which, when the light from the headlamps of another vehicle that is traveling near the vehicle in question is too strong, creates a dimming command to reduce the luminance of the headlamps of the other vehicle and send the command to the other vehicle.
However, the problem of the technology that is disclosed in JP-A-2002-193027 is that power consumption cannot be reduced because changing the luminance of the headlamps is not considered. In JP-A-2004-291816, a control procedure that includes a step in which the vehicle in question sends a command to dim the headlights to the other vehicle and a step in which the other vehicle dims its headlights to a luminance level that is not lower than lower limit luminance information as a lower limit is considered. However, the problem is that the vehicle cannot determine whether to dim its own headlights. In addition, there is no disclosure about how to dim the headlights in JP-A-2004-291816.
Conventionally, halogen lamps or discharge headlights are often used for headlamps, and it is, therefore, difficult to dynamically change the luminance of headlamps. However, the use of LED lamps (light-emitting diode lamps) with higher luminous efficiency in headlamps is gradually increasing. The luminance of LEDs can be changed easily even during driving, but variable control of the luminance of headlamps that use LEDs has not been considered.